The laminar organization of ganglion cell dendrites within the inner plexiform layer (IPL) is a major determinant of their response properties. Distinct subsets of ganglion cells possess unique dendritic morphologies, receive defined afferent connections from amacrine and bipolar cells, and project upon specific central targets ("Target Specific Ganglion Cells"). Their action on the central target is modulated by their neurotransmitters/modulators. Using immunohistochemical methods, we have demonstrated the existence of diverse populations of chemically specific amacrine cells in all classes of vertebrates. Most recently we have discovered the presence of four major peptides in distinct subsets of frog retinal ganglion cells. Each ganglion cell subset terminates in separate central targets. This project will study the laminar organization and interaction of amacrine cells and ganglion cells within the IPL of mammals and birds. The project consists of three parts: I. Contributions of chemically defined populations of amacrine and ganglion cells to lamination in the IPL. II. Dendritic morphology and transmitters of retinal ganglion cells terminating in the optic tectum. III. Identification of transmitter specific subsets of amacrine cells in receipt of centrifugal projections from the brain. These studies will help identify ganglion cell transmitters, and contribute to our understanding of the basic microcircuitry of the retinal organization. Methods to be used include IHC, cDNA in situ hybridization, single cell filling, EM and pathway tracing methods.